Two-part hitches installed on vehicles such as cars, vans and light trucks have become popular for towing trailers and other wheeled devices, and for mounting bicycle racks, wheel chair racks, and the like on the vehicle. An advantage is that the protruding shank which is removably installed in the hitch receiver, which is bolted to the frame of the vehicle, can be removed when not in use. Two-part hitches usually comprise a detachable drawbar, or equalizer hitch implement, or the like, which typically have either a hollow tube type shank or solid type shank. A solid shank is strong and durable and is preferred over a hollow tube type shank in heavy duty applications. The shank removably fits into a square tube hitch receiver which is permanently secured to the vehicle. The implement shank is secured to the hitch receiver by a detachable draw pin, which penetrates through holes in the hitch receiver and the shank. The draw pin holds the two parts together. When not in use, the implement shank can be detached from the hitch receiver on the towing vehicle by withdrawing the draw pin.
Typical methods of attaching implements with either hollow tube type shanks or solid shanks to square tube hitch receivers have many disadvantages. When a conventional securing or draw pin is used, the connection is not tight so there is undesirable movement between the implement shank and hitch receiver. This movement causes wear on both implement shank and hitch receiver. Excessive wear after time destroys the protective finish on both implement shank and hitch receiver, and allows rust to form causing serious problems when attempting to separate the implement shank and hitch receiver. Rust forms when the elements, rain, salt, road grit, etc., enter between the inner walls of the hitch receiver and the outer walls of the implement shank. The rust expands in the small space between the shank and the hitch receiver and solidifies, in effect making the two parts one solid piece. Attempts to prevent rust from forming include painting, plating, or greasing the shank. All of these rust prevention techniques are worn off very quickly due to the constant movement between the implement shank and hitch receiver, and thus do not prevent rust from forming over the long term.
It is also common for the holes in both the implement tube and the hitch receiver to become elongated over time due to frequent heavy load yanking of the implement shank in the hitch receiver. This is caused by the constant starting and stopping of the towing vehicle, and the momentum weight placed on the hitch, and in particular, concentrated on the pin and the hole. In the case of the solid shank, when a conventional securing or draw pin is used, it is common for the holes in only the hitch receiver to become elongated over time for the same reasons.
In the case of the hollow tube type shank, in an effort to reduce the slack and stabilize the implement, it is common practice to install a second apparatus such as a collar that may contain one or more bolts that are tightened against the outside of the square tube walls of the hitch receiver. Another alternative is to use a wedge-shaped device that is inserted between the walls of the square tube of the implement and the square tube of the hitch receiver. In the case of the solid shank used in heavy duty applications, stabilizing collars and wedges are seldom utilized in that they are light duty in nature.
Another problem with the conventional draw pin is that when towing undesirable movement between the implement shank and hitch receiver transfers undesirable "play" to the unit in tow, and in the case of any type of rack attached to the hitch receiver (i.e. bicycle rack), this movement is transferred to the rack and causes it to wobble. In the case of the hollow tube type shank, stabilizing collars/wedges are commonly used to solve this problem.
Apart from the problems where the hitch receiver becomes stretched and the draw pin holes elongated, there is a security problem associated with the conventional draw pin used in a two-part hitch. This is because the draw pin is easily removed and therefore makes an easy theft target. Locks for draw pins have been developed, but these locks are subject to corrosion from road grit, road salt and weather elements, and hence the locks become unworkable over time. Such locks are also easily broken or damaged, thereby rendering them ineffective.
Another problem with the hollow tube type shank implements and solid shank implements, and square tube hitch receivers is that in the case of the hollow tube type shank, both tubes become concave on the sides if a single long bolt is used to fasten the two parts together. In the case of the solid shank, only the hitch receiver tube will become concave if fastened in the same fashion. This occurs when the single bolt is passed through the sidewalks of both the implement shank and the hitch receiver. The long bolt is secured with a nut which is tightened from one side only. The tightening of the single nut on the long bolt forces the sidewalls of one, or both, tubes together. While such tightening will marginally reduce side to side slack and movement, it will not reduce up and down slack and movement. Further, the irregular distorted concave shape of one, or both, tubes may cause difficulty in attempting to separate the implement shank from the hitch receiver.